Re: [PATCH v3 08/13] s390/qdio_main: Use kzalloc() for the IRQ structure

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [High] s390/qdio: kzalloc() breaks strict hardware alignment for qib and chsc_page
--

commit 9f2f47b6eeaa2161812dfa4d13374862da2270d0
Author: Mike Rapoport (Microsoft) <rppt@kernel.org>
s390/qdio_main: Use kzalloc() for the IRQ structure

This commit modifies the memory allocation for the QDIO IRQ structure, 
switching from the page allocator to the slab allocator. It replaces 
get_zeroed_page() with kzalloc() and updates the free paths to use kfree(). 
It also removes a related kmemleak exemption.

Link: https://lore.kernel.org/all/635405e4-9423-4a25-a6e7-e03c8ea0bcbe@redhat.com

> diff --git a/drivers/s390/cio/qdio_main.c b/drivers/s390/cio/qdio_main.c
> index d137bf8c70664..28eb8602ca97e 100644
> --- a/drivers/s390/cio/qdio_main.c
> +++ b/drivers/s390/cio/qdio_main.c

[ ... ]

> @@ -961,7 +961,7 @@ int qdio_allocate(struct ccw_device *cdev, unsigned int no_input_qs,
>  	    no_output_qs > QDIO_MAX_QUEUES_PER_IRQ)
>  		return -EINVAL;
>  
> -	irq_ptr = (void *) get_zeroed_page(GFP_KERNEL);
> +	irq_ptr = kzalloc(PAGE_SIZE, GFP_KERNEL);

[Severity: High]
Does this kzalloc() replacement break the architectural alignment guarantees 
for the QDIO irq structure?

The irq_ptr contains a struct qib which has a strict 256-byte architectural
alignment requirement. Additionally, the irq_ptr->chsc_page allocated later
in qdio_allocate() (which was also converted to kzalloc in an earlier patch)
is passed to the CHSC instruction, which strictly mandates 4096-byte (page)
alignment.

When memory debugging features like CONFIG_SLUB_DEBUG (redzoning) or KASAN
are enabled, kzalloc() can return a pointer offset by the redzone size, 
breaking these 256-byte and 4096-byte structural alignment guarantees.

Could passing this unaligned memory to the CHSC hardware instruction 
trigger a hardware specification exception during device initialization?

>  	if (!irq_ptr)
>  		return -ENOMEM;
>

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260916-s390-cio-ready-v3-0-39e4894637d6@kernel.org?part=8